4.9 RETURN THERMISTOR FAULT
4.10 FAN FAULT
4.11 LOW WATER PRESSURE
Disconnect the electrical connection to the
Return Thermistor and check the resistance
using a suitable multimeter connected across the
thermistor’s terminal pins.
At 25°C expect 9,700 - 10,300 Ω
At 60°C expect 2,400 - 2,600 Ω
At 85°C expect 1,000 - 1,100 Ω
Is the thermistor value correct?
Does the wiring from the Fan to the PCB have
secure connections at both ends and has not
deteriorated?
Are the boiler and CH system lled with water and
all Isolation and Radiator Valves open?
Is there continuity in the wiring from the primary PCB to
the Thermistor? (8 way connector, connections 5 and
6, black and red)
Is there 240Vac at the blue and brown connections to
the 3 way connection on the Fan?
Does the wiring from the Water Pressure Switch to the
PCB have continuity and is it securely connected?
Replace primary PCB
Replace Fan
Replace Water Pressure Switch
Yes
Yes
Yes
No
No
Yes
Yes
No
Yes
No
No
No
Fit a new thermistor
Rectify wiring & connections
Fill and vent the system and open
all Isolation Valves
Replace wiring from ow thermistor to
primary PCB
Replace main PCB
Ensure wiring has continuity and is
securely connected
4.12 NO WATER FLOW
Are the boiler and CH system lled with water and
all Isolation and Radiator Valves open?
Does the mains wiring from the Pump to the main PCB
have continuity and is it securely connected (6 way
connector X2)?
Is there 230V to the Pump?
Replace Pump
No
No
No
Yes
Yes
Yes
Fill and vent the system and open all
Isolation Valves
Ensure wiring has continuity and is
securely connected
Replace Main PCB
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